Before society became concerned with various kinds of environmental pollution, it was common for industries to dump production waste products into rivers, lakes, streams or special ponds. Some of these waste materials included highly toxic metal ions such as lead, cadmium, barium, mercury, and copper to name just a few.
One past method of cleaning water contaminated with heavy metal ions involved pumping the water into a holding tank and adding precipitating agents such as calcium hydroxide and flocculating chemicals such as alum. The resultant sludge was removed by settling or filtering and buried in a landfill.
Another method of decontaminating water involves pumping the water through a mass of ion exchange beads to a holding tank.
Both of the foregoing methods are expensive because they require pumping of massive amounts of water. Sludge burial is no longer acceptable because landfills are running out of space. Accordingly, there is a need for the capability of removing heavy metal ions from water or water containing mixtures without transferring water between sites.
It has been found that ion exchange membranes or films disposed in bodies of water polluted with heavy metals will attract heavy metal ions. The membranes or films can be cleansed of the heavy metal ions by various methods such as acid treatment. The ion exchange membranes must be insoluble in water.
Ion exchange membranes are known in the prior art and include particularly battery separators. In order to avoid the use of asbestos, state of the art battery separators use various polymers. Cross-linking of these polymers is accomplished by techniques such as heating or irradiation by electromagnetic waves such as ultraviolet radiation. Chemical methods of cross-linking are also used.
U.S. Pat. No. 3,872,001 teaches making an acid-containing porous polymer wherein a chelate-divalent metal complex has been reacted with the acid groups. Polluted water is directed through the porous polymer.
U.S. Pat. No. 4,357,402 discloses that a polyvinyl alcohol resin can be mixed, in aqueous solution, with a dialdehyde cross-linking agent and a water soluble acid aldehyde. The mixture is heated to dry and cross-link it.
U.S. Pat. No. 4,298,698 teaches that an alkali salt or an alkaline earth salt of an .alpha.-alkyl acrylate can be dispersed in a hydrophilic polymer. The ingredients are subjected to ionizing radiation to effect cross-linking thereby forming an ion exchange membrane.
U.S. Pat. No. 4,377,481 discloses a polymeric membrane comprising a water-insoluble matrix polymer arid a water insoluble copolymer containing an acrylate or a methacrylate first monomer and a second monomer such as a carboxylic group which contributes hydrophilic properties to the blended membrane.
U.S. Pat. No. 2,783,212 discloses a cation exchange membrane comprising a polymerizable water soluble organic acid such as acrylic acid or methacrylic acid; a polymerizable organic compound containing at least two polymerizable double bonds in the presence of a polymerizable catalyst; and, a compound selected from the group consisting of polyhydric alcohols, polyamines or aldehydes.